Symptoms are caused by inflammation of the blood vessels, particularly veins. Inflammation is the body’s characteristic reaction to injury or disease and is marked by four signs: swelling, redness, heat, and pain. Doctors think that an autoimmune reaction may cause blood vessels to become inflamed, but they do not know what triggers this reaction.

Consequences of Behcet's Disease
If the arteries become inflamed from Behcet's syndrome, it can lead to death of the tissues whose oxygen supply depends on these vessels. This could cause a stroke if it is affecting the brain vessels, belly pain if affecting the bowel, etc. When veins become inflamed, the inflammation can involve large veins that develop blood clots which can loosen and migrate to cause pulmonary embolisms. Symptoms of inflammation of the brain or tissue that covers the brain include headaches, neck stiffness, and is often associated with fever. Inflammation of the brain or the meninges can cause damage to nervous tissue and lead to weakness or impaired function of portions of the body. This can result in confusion and coma. Typically these features occur later in the disease course, years after the diagnosis.

Joint inflammation can lead to swelling, stiffness, warmth, pain, and tenderness of joints with Behcet's syndrome. This occurs in about half of patients with Behcet's syndrome at sometime during their lives. Knees, wrists, ankles, and elbows are the most common joints affected. The skin of patients with Beh?et's syndrome can develop areas of inflammation that spontaneously appear as raised, tender, reddish nodules, typically on the front of the legs. Some patients with Behcet's syndrome develop a peculiar red or blistery skin reaction in places where they have been pierced by blood-drawing needles. Research has found that acne occurs more frequently in patients with Behcet's syndrome that also have arthritis as a manifestation.